The present invention relates to an interconnect alignment system for use with optical and opto-electronic systems. More particularly, the present invention relates to a device for providing alignment control during mating of an optical or opto-electronic connector system.
Cabinets traditionally used for electronic devices are now being utilized to accommodate optical and opto-electronic devices. In traditional cabinet designs, the cabinet comprises a box having a plurality of internal slots (also known as racks), generally parallel to each other. Components are mounted on planar substrates (commonly referred to as circuit boards or daughter cards, or simply boards or cards) which are designed to slide into the slots within the cabinet. As a card is inserted into the slots within the cabinet, mechanical, electrical and/or optical connections are formed with mating components in the cabinet.
Mating components in the cabinet are typically on a backplane in the cabinet. A backplane derives its name from the back (distal) plane in a parallelepipedal cabinet and generally is orthogonal to the plane of the inserted card. The term backplane as used in connection with the present invention refers to an interconnection plane where a multiplicity of interconnections may be made, such as with a common bus or other external device. For explanation purposes, a backplane is described as having a front or interior face and a back or exterior face.
An example of a backplane connectivity application is the interconnection of telephone switching equipment. In this application, cards having optical and electronic telecommunication components are slid into cabinets. As a function of inserting and removing a card from a rack coupled to the backplane, coupling and uncoupling of the electrical and optical connections in the card must be completed in a blind mating manner.
To maintain appropriate transmission of light signals in an optical connection, optical fiber ends should be carefully aligned along all three linear movement axes (x, y, and z), as well as aligned angularly. Alignment challenges increase and dimensional tolerances decrease as the number of optical fibers to be aligned increases. Blind mating of a card-mounted component to a backplane connector has been found to create special challenges with regards to alignment and mating force issues along the axis of interconnection.
For the purposes of the present description, the axis of interconnection is called the longitudinal or x-axis and is defined by the longitudinal alignment of the optical fibers at the point of connection. Generally, in backplane applications, the longitudinal axis is collinear with the axis of movement of the cards and the axis of connection of the optical fibers in and out of the cabinets. The lateral or y-axis is defined by the perpendicular to the x-axis and the planar surface of the card. Finally, the transverse or z-axis is defined by the orthogonal to the x-axis and the backplane surface. The angular alignment is defined as the angular orientation of the card with respect to the x-axis.
Ideally, the motion of sliding the card into a receiving slot simultaneously achieves optical and/or electrical interconnection between the card components and the backplane. However, dimensional tolerances of the cards, the components thereon and the slots themselves may result in excessive movement or “play” of a card in a slot. Thus, when an operator inserts a card in a slot, it is often difficult to maintain the leading card edge and components thereon in correct alignment with the axes of the backplane.
To achieve a good interconnection, the card components should be properly aligned along the longitudinal, lateral and transverse axes with the mating components on the backplane as the card is inserted in the slot. Longitudinal misalignment influences the “optical gap” (the distance along the longitudinal axis between the optical fiber ends of interconnected optical components). An optical gap will degrade the connection, resulting in the loss or degradation of the optical signals and creates undesirable internal reflecting. On the other hand, excessive pressure on the mating faces, such as that caused by “jamming in” a card, may result in damage to the fragile optical fiber ends and mating components. Traditional optical gap tolerances are in the order of less than one micron. Lateral and transverse misalignment influence the ability to make an interconnection at all. If the card is sufficiently misaligned along the lateral or transverse axis, stubbing of the mating connector halves may occur and interconnection may be prevented completely. FIG. 1A illustrates a linearly misaligned card 10 having a connector 12 mating to a backplane connector 14. In FIG. 1A, the card 10 is grossly misaligned along the lateral (y) axis such that optical fibers 16 are not properly aligned and interconnection is prevented.
Another consideration is angular misalignment of the card. FIG. 1B illustrates angularly misaligned card 10. The card is otherwise correctly aligned along the y and z-axes. At the point of contact between connectors 12 and 14, the angular misalignment prevents correct optical gap spacing between optical fibers 16 and causes undue pressure on one end of the connector and the respective optical fiber end faces.
An additional subject of concern is “card gap”, especially when dealing with backplane connector systems. Card gap is defined as the space remaining between the rear edge of a card and the interior or front face of the backplane. In general, designers and users of backplane connection systems find it exceedingly difficult to control the position of a card to a backplane within the precision range required for optical interconnects. Card gap, otherwise defined as card insertion distance, is subject to a multiplicity of variables. Among these variables are card length, component position on the surface of the card, card latch tolerances, and component position on the backplane.
Over-insertion of a card relative to the interior surface of a backplane presents a separate set of conditions wherein the backplane connector's components are subjected to excessive compressive stress when fixed in a mated condition. In certain instances the compressive stress may be sufficient to cause physical damage to the connector's components and the optical fibers contained therein.
The need remains for a connector system that prevents component damage due to excessive operator force, compensates for linear card misalignment, yet provides accurate control of optical gap distance and mating force.